1. Field of the Invention
The present invention relates in general to a method and apparatus for determining attitude of an artificial satellite (hereinafter referred to simply as a satellite). In particular, the invention concerns such method and apparatus in which a star sensor is employed.
2. Description of the Prior Art
In a hitherto known satellite attitude determining system in which a star sensor is employed, the attitude of a satellite is measured with a relatively rough accuracy on the basis of information provided by attitude measuring sensors, such as gyros, earth sensors or the like, and star identification is made between the stars observed by the star sensor and those which are located in a predetermined region of the whole sky by making use of the attitude angle data obtained with rough accuracy. This is because there are as many as 6000 stars having brightness greater than the sixth stellar magnitude in the whole sky and great time consumption is involved if the star identification is made for each of these stars, respectively, putting aside the fact that a memory of a great capacity which is not suited to be loaded on the satellite is required. Such being the circumstance, the use of the star sensor has been limited to such application in which the satellite attitude is to be measured the using a star sensor in combination with another sensor with a high accuracy on the condition that the attitude of the satellite is stable.